System for combined transcutaneous blood gas monitoring and vacuum assisted wound closure

ABSTRACT

A method and apparatus for the transcutaneous monitoring of blood gases generally comprises a blood gas data acquisition device, a vacuum source and a blood gas transducer unit. The blood gas transducer unit is adapted for application to a patient&#39;s skin and administration of a local vacuum at the area of patient application. It further comprises an electrochemical blood gas transducer, well known to those of ordinary skill in the art, which is disposed entirely within the local vacuum at the area of patient application. The vacuum source is placed in fluid communication with the blood gas transducer unit, through a hydrophobic membrane filter for safety purposes, in order to induce a condition of hyperperfusion in the locality of the electrochemical blood gas transducer. Under the control of a microcontroller, or equivalent means, the blood gas acquisition device is then utilized to capture a measure of skin surface oxygen or carbon dioxide pressure. The microcontroller can then utilize this measure to arrive at an estimate of arterial partial pressure of oxygen or carbon dioxide, accordingly. Because vacuum induced perfusion produces the requisite condition of hyperperfusion without local heating and, therefore, without acceleration of the local metabolic function, the present invention results in more accurate than previously available estimates of partial pressure blood gas pressures and does so while eliminating a significant risk for injury to the patient.

RELATED APPLICATIONS

[0001] This application is a continuation-in-Part, of co-pending U.S.patent application Ser. No. 09/579,755, entitled “Transcutaneous BloodGas Monitoring with Vacuum Pefusion,” filed on May 26, 2000.

FIELD OF THE INVENTION

[0002] The present invention relates to the monitoring of blood gasesduring vacuum assisted wound healing. More particularly, the inventionrelates to a method and system for the transcutaneous monitoring ofblood gases wherein said monitoring is enhanced by application of avacuum pressure in the region of skin under evaluation, and during whichnegative pressure therapy is being applied to an adjacent or proximalwound site.

BACKGROUND OF THE INVENTION

[0003] Transcutaneous blood gas monitoring is known in the relevant artsas a method by which measurements of skin-surface gas pressures may beutilized to estimate arterial partial pressures of the gas of interest.In particular, skin surface oxygen or carbon dioxide pressure PO₂ orPCO₂, respectively, is measured by a locally applied, electrochemicallybased device in order to develop an estimate of arterial partialpressure of oxygen or carbon dioxide P_(a)O₂ or P_(a)CO₂, respectively.The obtained estimate is then made available to the clinician as an aidfor the routine or emergency assessment of any of a variety of knowncardiopulmonary functions.

[0004] In practice, a condition of hyperperfusion is indicated in theregion of skin adjacent the applied device in order to enhance the flowof arterial blood gases toward and through the skin surface. To date,this hyperperfusion condition has been established by local heating ofthe skin with an electrode in order to distend the arterial capillaries.Unfortunately, such local heating carries with it an increased risk fortissue injury—erythema, blisters, burns and skin tears being among thedocumented complications. In addition, some debate exists within the artas to whether the increased local metabolic rate concomitant theapplication of heat counteracts the intended perfusion effect. If so,false readings may result, which may ultimately lead to inappropriatetreatment of the patient.

[0005] The use of transcutaneous blood gas monitoring can beparticularly advantageous when used in conjunction with negativepressure therapy for vacuum induced healing of open wounds or othertissue damage. Vacuum induced healing of open wounds has recently beenpopularized by Kinetic Concepts, Inc. of San Antonio, Tex., by itscommercially available V.A.C.® product line. The vacuum induced healingprocess has been described in commonly assigned U.S. Pat. No. 4,969,880issued on Nov. 13, 1990 to Zamierowski, as well as its continuations andcontinuations in part, U.S. Pat. No. 5,100,396, issued on Mar. 31 1992,U.S. Pat. No. 5,261,893, issued Nov. 16, 1993, and U.S. Pat. No.5,527,293, issued Jun. 18, 1996, the disclosures of which areincorporated herein by this reference. Further improvements andmodifications of the vacuum induced healing process are also describedin U.S. Pat. No. 6,071,267, issued on Jun. 6, 2000 to Zamierowski andU.S. Pat. Nos. 5,636,643 and 5,645,081 issued to Argenta et al. on Jun.10, 1997 and Jul. 8, 1997 respectively, the disclosures of which areincorporated by reference as though fully set forth herein. Additionalimprovements have also been described in U.S. Pat. No. 6,142,982, issuedon May 13, 1998 to Hunt, et al.

[0006] The use of transcutaneous blood gas monitoring in conjunctionwith V.A.C.® therapy allows for monitoring of blood gases within andaround the wound bed. Blood gases can be an indicative factor of woundhealing progression. Crucial information can be ascertained as to theprogression of the wound without disturbing the wound dressing.

[0007] It is therefore a primary object of the present invention toimprove over the prior art by providing a method and apparatus for thetranscutaneous monitoring of blood gases wherein local heating forhyperperfusion is eliminated, thereby eliminating a significant patienthazard and wherein the concomitant metabolic effects of local heatingare likewise eliminated, thereby reducing the likelihood formisdiagnosis leading to inappropriate treatment regimen.

[0008] Hyperperfusion through local heating also requires a prolongedwarm up and stabilization time following electrode placement in orderfor equilibration and calibration of the electrochemical transducer. Asa result, operator time is generally wasted in the administration of atranscutaneous blood gas evaluation. Additionally, transcutaneous bloodgas monitors are either not available for emergency use or must be madeavailable with an operated in a standby mode. Such a standby moderequires additional hardware and generally shortens the electrodelifecycle.

[0009] It is therefore a further object of the present invention toimprove over the prior art by providing a method and apparatus for thetranscutaneous monitoring of blood gases wherein the apparatus isavailable for full operation on short notice without requirement foradditional and/or lifecycle shortening hardware.

[0010] It is still a further object of the present invention to providea system and method that combines the advantages of a non-invasive bloodgas monitoring device with the effectiveness of negative pressuretherapy upon wounds, so as to further improve the efficacy of negativepressure therapy on the treatment of wounds and other tissue treatments.

[0011] Finally it is still a further object of the present invention toimprove over the prior art by providing a method and apparatus for thetranscutaneous monitoring of blood gases wherein the above-describedobjects are implemented without sacrifice to patient safety or deviceefficacy, but wherein unnecessary hardware and software is nonethelessavoided, thereby conserving the ever more limited healthcare dollar.

SUMMARY OF THE INVENTION

[0012] In accordance with the foregoing objects, the present invention—amethod and system for the transcutaneous monitoring of blood gases andvacuum assisted wound closure-generally comprises a blood gas dataacquisition device, a vacuum source and a blood gas transducer unit. Theblood gas tansducer is adapted for application to a patient's skin andadministration of a local vacuum at the area of patient application. Itfurther comprises an electrochemical blood gas tranducer, well known tothose of ordinary skill in the art, which is disposed entirely withinthe local vacuum at the area of patient application. The transducer mayalso be disposed within a wound site, or an area immediately adjacent awound site that is being treated by negative pressure therapy. The useof negative pressure therapy may include a porous, semi-rigid screenplaced within a wound bed, a cover for maintaining a negative pressurewithin the wound bed that is placed over the screen and wound bed, and avacuum source in fluid communication with the screen. Additionally, acanister may be disposed between the screen and vacuum source, for thecollection of fluids that may eminate from the wound during applicationof negative pressure by the vacuum source. A flexible tube or similardevice is used to communicate between the screen and vacuum source.

[0013] It is contemplated that the transducer may be incorporated withinthe screen, or alternatively placed as a separate element below thescreen to be in direct contact with the wound bed, within a depressionor cut-out of the screen, above the screen, or separate from the screenbut immediately adjacent the wound bed.

[0014] The blood gas transducer unit is in fluid communication with thevacuum source through an interposed vacuum hose and in electricalcommunication with the blood gas data acquisition device through aninterposed electrical cable. The vacuum source, which comprises a vacuumpump operated by a pump motor is placed in fluid communication with theblood gas transducer unit in order to induce a condition ofhyperperfusion in the locality of the electrochemical blood hastransducer. Under the control of the microcontroller, or equivalentmeans, the blood gas data acquisition device is then utilized to capturethis measure to arrive at an estimate of arterial partial pressure ofoxygen or carbon dioxide, accordingly. Because vacuum induced perfusionproduces the requisite condition of hyperperfusion without local heatingand, therefore, without acceleration of the local metabolic function,the present invention results in more accurate than previously availableestimates of partial blood gas pressures and does so while eliminating asignificant risk for injury to the patient.

[0015] The same vacuum source, or alternatively a second vacuum source,may be utilized to provide negative pressure at the wound site bycommunicating with the screen placed within the wound site, by means ofa tube or similar device.

[0016] Because the application of vacuum perfusion to the patientpresents at least some risk for contamination of the vacuum source andblood gas data acquisition device, the preferred embodiment of thepresent invention further comprises a tranducer interface moduleparticularly adapted for the reduction or elimination of contaminationrisk. According to the invention, the transducer interface modulecomprises a male and female interface pair, wherein the male portion isadapted into the female portion and thereby establish communicationbetween the blood gas transducer unit and the vacuum source and bloodgas data acquisition device.

[0017] In implementing the male plug, a hydrophobic membranefilter—known to those of ordinary skill in the art—is interposed in thevacuum hose, thereby eliminating the opportunity for contaminants topass from the patient to the vacuum source or blood gas data acquisitiondevice. While the preferred embodiment of the present inventioncomprises a throw-away male plug, vacuum hose, electrical cable andblood gas transducer unit, those of ordinary skill in the art willrecognize that each of these components can be made reusable withimplementation of proper, known sterilization techniques. In this lattercase, the hydrophobic membrane filter is preferably replaceable.

[0018] Finally, many other features, objects and advantages of thepresent invention will be apparent to those of ordinary skill in therelevant arts, especially in light of the foregoing discussions and thefollowing drawings and exemplary detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] These and other features and advantages of the invention will nowbe described with reference to the drawings of certain preferredembodiments, which are intended to illustrate and not to limit theinvention, and wherein like reference numbers refer to like components,and in which:

[0020]FIG. 1 shows, in perspective view, the preferred embodiment of thetranscutaneous blood gas monitoring apparatus of the present invention,as employed with a human subject;

[0021]FIG. 2 shows, in schematic block diagram, details of the apparatusof FIG. 1; and

[0022]FIG. 3 shows, in schematic block diagram, a transcutaneous bloodgas monitoring device utilized in conjunction with a negative pressuretherapy device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] Although those of ordinary skill in the art will readilyrecognize many alternative embodiments, especially in light of theillustrations provided herein, this detailed description is exemplary ofthe preferred embodiment of the present invention, the scope of which islimited only by the claims that may be drawn hereto.

[0024] Referring now to FIG. 1, the preferred embodiment of thetranscutaneous blood gas monitoring system 10 of the present inventionis shown to generally comprise a blood gas data acquisition device 11, avacuum source 12 and a blood gas transducer unit 13. As shown in FIG. 1,the blood gas transducer unit 13 is adapted for application to apatient's skin 14. In alternative embodiments, not shown, the blood gastransducer may be applied within a wound bed 30 or disposed within ascreen 32 placed within the wound bed 30. As will be better understoodfurther herein, the blood gas transducer unit 13 is also adapted foradministration of a local vacuum at the area of the patient application.Finally, the blood gas transducer unit 13 comprises an electrochemicalblood gas transducer 15, well known to those of ordinary skill in theart, which is disposed entirely within the local vacuum at the area ofpatient application.

[0025] As also depicted in FIG. 1, the blood gas transducer unit 13 isin fluid communication with the vacuum source 12 through an interposedvacuum hose 16 and in electrical communication with the blood gas dataacquisition device 11 through an interposed electrical cable 17.Although those of ordinary skill in the art will recognize manysubstantial equivalents, the preferred embodiment of the presentinvention comprises a unitary hose and cable pair 18. Such a unitarypair 18 serves to reduce clutter in the patient care environment,thereby reducing the likelihood of either the hose 16 or cable 17becoming entangled with other tubes, cables or equipment. Further, andas will be better understood further herein, such a unitary pair 18 isespecially adapted for use with the preferred embodiment of the noveltransducer interface module 19 of the present invention.

[0026] According to the preferred embodiment of the present invention,the vacuum source 12 comprises a vacuum pump 20 operated by a pump motor21. Those of ordinary skill in the art, however, will recognize manysubstantially equivalent embodiments for the vacuum source 12 including,for example, a central hospital vacuum or suction source or an integralpump and motor. In any case, all such equivalents are considered withinthe scope of the invention, which requires only a vacuum source 12 ofthe character otherwise described herein, and which is capable ofproviding suction in the range of about 50 mmHg through 250 mmHg.

[0027] In operation, the vacuum source 12 is placed in fluidcommunication with the blood gas transducer unit 13 in order to induce acondition of hyperperfusion in the locality of the electrochemical bloodgas transducer 15. Under the control of a microcontroller 22, orequivalent means, the blood gas data acquisition device 11 is thenutilized to capture a measure of skin surface oxygen or carbon dioxidepressure. The microcontroller 22 can then utilize this measure to arriveat an estimate of arterial partial pressure of oxygen or carbon dioxide,accordingly. Because vacuum induced perfusion produces the requisitecondition of hyperperfusion without local heating and, therefore,without acceleration of the local metabolic function, the presentinvention results in more accurate than previously available estimatesof parial blood gas pressures and does so while eliminating asignificant risk for injury to the patient.

[0028] Because the application of vacuum to the patient presents atleast some risk for contamination of the vacuum source 12 and blood gasdata acquisition device 11, the preferred embodiment of the presentinvention further comprises a transducer interface module 19particularly adapted for the reduction or elimination of contaminationrisk. According to the invention, the transducer interface module 19comprises a male 23 and female 24 interface pair, wherein the maleportion 23 is adapted to plug into the female portion 24 and therebyestablish communication between the blood gas transducer unit 13 and thevacuum source 12 and blood gas acquisition device 11.

[0029] In implementing the male plug 23, a hydrophobic membrane filter25—known to those of ordinary skill in the art—is interposed in thevacuum hose 16, thereby eliminating the opportunity for contaminants topass from the patient 14 to the vacuum source 12 or blood gas dataacquisition device 11. While the preferred embodiment of the presentinvention comprises a throw-away male plug 23, vacuum hose 16,electrical cable 17 and blood gas transducer unit 13, those of ordinaryskill in the art will recognize that each of these components can bemade reusable with implementation of proper, known sterilizationtechniques. In this latter case, the hydrophobic membrane filter 25 ispreferably replaceable.

[0030] Referring now to FIG. 3, a collection canister 34 may beinterposed between the vacuum source 12 and the screen 32. As suction isapplied, fluids may be drawn from the wound 30 and collected in thecanister 34. A common vacuum source 12 may be utilized to provide vacuumperfusion to the blood gas transducer 13 and negative pressure to thewound site 30. A seal 36 is adhered over the screen 32 in order tomaintain negative pressure within the wound site 30. The seal 36 may becomprised of a an elastomeric material. The screen 32 is preferablycomprised of poly-vinyl alcohol foam, or alternatively a polyurethaneporous sheet. It is to be understood that any semi-rigid and porousmaterial may utilized as a screen 32 within the wound bed 30. The tube16 may be in direct fluid communication with the screen 32 (not shown),or connected to an adapter 38 that is adhered over an opening 40 in theseal 36. It is preferable that the tube 16 is bifurcated at a positionbetween the vacuum source 12 and the canister 34 so that fluids beingdrawn from the wound site 30 do not interfere with the vacuum perfusionof the blood gas transducer 13.

[0031] In an alternate embodiment, not shown, a separate vacuum sourcemay be utilized to provide negative pressure to the wound site 30 andanother vacuum source utilized to provide vacuum perfusion to the bloodgas transducer 13.

[0032] While the foregoing description is exemplary of the preferredembodiment of the present invention, those of ordinary skill in therelevant arts will recognize the many variations, alterations,modifications, substitutions and the like as are readily possible,especially in light of this description and the accompanying drawings.For example, a membrane or other like switch pad 26 may be implementedfor user control of the transcutaneous blood gas monitor 10 and/or adisplay, printer or other output device 27 may be provided formonitoring and/or recording of estimated partial pressures. Likewise, apressure transducer 28 may be, and preferably is, provided formonitoring and control of the vacuum applied to the patient 14. In anycase, because the scope of the present invention is much broader thanany particular embodiment, the foregoing detailed description should notbe construed as a limitation of the scope of the present invention,which is limited only by the claims that may be drawn hereto.

What is claimed is:
 1. A transcutaneous blood gas monitoring deviceparticularly suited for application to a site on a patient's skin undera local vacuum, comprising: a non-invasive blood gas data acquisitiondevice; a vacuum source; and an electrochemical blood gas transducerunit in fluid communication with said vacuum source.
 2. Thetranscutaneous blood gas monitoring device of claim 1 wherein saidvacuum source is in fluid communication with a wound site in proximityto said site on patient's skin for applying a negative pressure to saidwound site.
 3. The transcutaneous blood gas monitoring device of claim 2further comprising: a screen means formed to fit within said wound site,such that said screen means is in fluid communication with said vacuumsource; a sealing means for maintaining a negative pressure within saidwound site during application of said negative pressure.
 4. Thetranscutaneous blood gas monitoring device of claim 2 wherein said dataacquisition device monitors healing of said wound site.
 5. Thetranscutaneous blood gas monitoring device of claim 1 further comprisinga controller for governing actions of said device.